1. Field
The disclosure relates to a composition useful in encapsulating thin film devices. The disclosure also relates to a method of encapsulating thin film devices with the composition and to devices produced by the method.
2. Description of the Related Art
Polymeric materials are used in the construction of photovoltaic modules to protect cells, provide electrical isolation, and prevent environmental corrosion. Due to a combination of mechanical properties and attractive price, ethylene vinyl acetate (EVA) polymer-based encapsulants from various suppliers represent a significant majority of the materials used.
One of the long-standing complaints regarding EVA polymers and copolymers is the potential for the generation of corrosive acetic acid upon exposure to atmospheric moisture and/or ultraviolet radiation. This has not proven to be a significant drawback with crystalline silicon cells, and given the low potential percentages of acid generated, coupled with a slow rate of generation, it appears unlikely that acid build-up would be an issue in an construction utilizing a “breathable” back-sheet construction, i.e. Tedlar®/polyester/Tedlar® (TPT) or laminated polyester.
With the rise in silicon prices, however, there has been an increase in the types of non-crystalline devices and the number of modules produces with these technologies. While these devices can offer significant cost savings they are more prone to damage from the environment in the form of moisture and are more sensitive to the potential effects of acetic acid build-up.
Because water alone can be problematic for vapor-deposited devices such as amorphous silicon, most of these constructions rely on a “non-breathable” backside, typically glass. While there is some disagreement within the industry as to the significance of acetic acid, and a large number of modules are produced daily with EVA polymer-based encapsulants, there are also legitimate reasons for concern and the need for a material that eliminates the acid issue is clear. A number of non-EVA encapsulants are in use commercially, such as those based on silicones, polyvinyl butyral (PVB) and ionomeric polymers. Most suffer in some way when compared to EVA, such as in moisture vapor transmission rate (MVTR) or ease of use, and all are significantly more expensive.
Given the importance of increasing the durability of thin-film devices while keeping costs as low as possible, it is desirable to develop a non-EVA based encapsulants that offer the ease of use and low cost found with EVA. It would further be advantageous if the encapsulants provide good moisture protection and/or corrosion protection, particularly when used with vapor deposited modules.